Status and R&D development of Photon Calorimeter G. Atoian, S. Dhawan, V. Issakov, A. Poblaguev, M. Zeller, Physics Department, Yale University, New Haven, CT G.I. Britvich, S. Chernichenko, I. Shein and A. Soldatov Institute for High Energy Physics, Protvino, Russia O. Karavichev, T. Karavicheva and V. Marin Institute for Nuclear Research of Russian Academy of Sciences, Moscow, Russia

Photon Calorimeter for KOPIO The requirements of the KOPIO Photon Calorimeter: Energy resolution -  3[%]/  E. Time resolution -  90[psec]/  E. Photon detection inefficiency (due to holes-cracks) -  Active area  5.3 m 2 Granularity - 11  11 cm 2. Radiation length - 16X 0 (18X 0 including Preradiator). Physical length -  60 cm. The Shashlyk technique satisfies the KOPIO requirements. All sizes are millimeters

The design innovations: New scintillator tile (BASF143E + 1.5%pTP %POPOP produced by IHEP) with improved optical transparency and improved surface quality. The light yield is now ~ 60 photons per 1 MeV of incident photon energy. Nonuniformity of light response across the module is <2.3% for a point-like light source, and < 0.5% if averaged over the photon shower.. New mechanical design of a module has four special "LEGO type" locks for scintillator’s tiles. These locks fix the position of the scintillator tiles with the 300-  m gaps, providing a sufficient room for the 275  m lead tiles without optical contact between lead and scintillator. The new mechanical structure permits removing of 600 paper tiles between scintillator and lead, reduces the diameter of fiber’s hole to 1.3 mm, and removes the compressing steel tape. The effective radiation length X 0 was decreased from 3.9 cm to 3.4 cm. The hole/crack and other insensitive areas were reduced from 2.5 % up to 1.6 %. The module’s mechanical properties such as dimensional tolerances and constructive stiffness were significantly improved. New photodetector Avalanche Photo Diode ( produced by Advanced Photonix Inc. ) with high quantum efficiency (~93%), good photo cathode uniformity (nonuniformity  3%) and good short- and long-term stability. A typical APD gain is 200, an excess noise factor is ~ 2.4. The effective light yield of a module became ~24 photoelectrons per 1 MeV of the incident photon energy resulting in negligible photo statistic contribution to the energy resolution of the calorimeter. Design of Calorimeter modules The calorimeter module is a very fine sampling “Shashlyk” structure consisting of 300 alternating layers of 275  m- thick lead tiles and 1.5 mm-thick scintillator tiles, which are penetrated by 144 Wave Length Shifting (WLS) fibers for a light readout.

Calorimeter module Lateral segmentation 110  110 mm 2 Scintillator thickness1.5 mm Gap between scintillator tiles0.300 mm Lead absorber thickness0.275 mm Number of the absorber layers (Lead/Scint)300 WLS fibers per module 72  1.5 = 108 m Fiber spacing9.3 mm Holes diameter in Scintillator/Lead1.3 mm/1.4 mm Diameter of WLS fiber (Y11-200MS)1.0 mm Fiber bundle diameter14.0 mm External wrapping (TYVEK paper) 150  Effective X o 34.0 mm Effective R M 59.8 mm Effective density2.75 g/cm 3 Active depth540 mm (15.9 X o ) Total depth (without Photodetector)650 mm Total weight18.0 kG

IHEP-KOPIO scintillator facility

Development of scintillator Scintillator: PS+Fluor1+Fluor2, Manufacturer Light yield (% of Anthracene) Attenuation Length (cm) Light yield of MIP, p.e. per tile Simulated light collection efficiency PSM %pTP+0.04%POPOP, TECHNOPLAST,  64.5   0.3, 100%  0.013, 100% BASF158K+1.5%pTP+0.04%POPOP, IHEP,  65.1   0.3, (127  10)%  0.017, (127  13)% BASF165H+1.5%pTP+0.04%POPOP, IHEP,  65.3   0.3 (145  10)%  0.019, (143  14)% BASF143E+1.5%pTP+0.04%POPOP, IHEP,  65.5   0.3, (161  10)%  0.021, (160  16)%

APD readout APD LV - HV Preamp

Beam test of Calorimeter prototypes Studied prototypes 1st prototype of 3  3 modules: The conventional design of modules (with paper between lead and scintillator); A 30 mm diameter 9903B PMT (Electron Tube Inc.) ; The conventional 12-bits ADC digitizing of the PMT signal. 2nd prototype of 3  3 modules: New design of modules (no paper between lead and scintillator); A 16 mm diameter APD (Advanced Photonix Inc.) ; An 8-bits 140 MHz WFD and 12-bits ADC digitizing of the APD signal. Measurements Beam intensity was ~ 3  10 5 Hz. Triggered and tagged photon energy was in the range MeV. Beam angle spread was ~ 2 mrad. Diameter of the beam spot at the prototype was ~ 1.5 cm. Photon energy spread was  E/E  1.5% (for the triggered and tagged monochromatic photon energy line). Two KOPIO calorimeter prototypes were tested at the Laser Electron Gamma Source (LEGS) facility at BNL NSLS. The energy resolution was measured for both prototypes with the beam in the center of nonet. The time resolution was studied for the 2nd prototype (with WFD only), comparing timing in two modules when the beam is between the two. The photon detection inefficiency was measured by the detecting photons in Prototype 1 located behind Prototype 2. The stability of the Calorimeter signals was tested by a LED monitoring system during the 24-hours measurements

Beam test of Calorimeter prototypes

The best results were achieved for prototype 2 with APD/WFD readout: Energy resolution  (2.9±0.1)%  E(GeV). Time resolution  (90±10)psec  E(GeV). Photon detection inefficiency  5  (for incident beam angle  5 mrad ). APD gain stability  1% (for tested period of 24 hours).

Simulation of the Shashlyk Calorimeter The simulation of the Shashlyk calorimeter in KOPIO is based on a GEANT3 description of the development of the electromagnetic shower, and an Optical Model for the simulation of the light collection in the scintillator tile. The GEANT3 part of the simulation includes a detailed description of the geometry of the Shashlyk module. Calculations are performed with low energy cuts 10 KeV and with delta-ray simulations to obtain consistency with experimental results. The Optical Model uses the tracking of the single photons in the scintillator tile. The parameters which customize the model, such as attenuation lengths, reflection efficiencies, the probability of photon capture in the fiber, were adjusted using optical measurements. The effects of light to photoelectron conversion and noise in the photodetector-preamplifier chain were also taken into account. The results of the simulation of the energy resolution are in excellent agreement with the experimental measurements in a range of photon and positron energies GeV. Experiment vs GEANT/OPTIC simulation

R&D plans for Calorimeter (2004) Development of the photodetector HV system ($15k): A sample of the APD HV "built-in" unit with a new LV-HV converter (C20) produced by EMCO HIGH VOLTAGE CORPORATION was tested. This HV supply with digital control provides very low ripple, high stability and low pick-up noise. The 25-channel prototype of this HV system will be build and tested with the new Calorimeter prototype.

R&D plans for Calorimeter (2004) Development of the photodetector cooling system ($15k): A tested APD cooling system: An improved prototype of the cooling system will provide the APD noise of 0.2  0.3 MeV (at 10 o C). Room temperature (21  28) o C APD temperature~ 18 o C Improvement of a signal/noise ratio (1.3  1.5) Equivalent Noise~ 0.5 MeV APD gain stability  1%

R&D plans for Calorimeter (2004) Development of the LED monitoring system ($15k): A 64-channel LED monitoring system will be built and tested with the new Calorimeter prototype. Temperature stability  0.1% Duration of the light pulse  20 nsec Variation of the flash amplitude  0.1 %; Photon intensity  10,000 p./ch. Pulse rateUp to 1 MHz

R&D plans for Calorimeter (2004) Development of the photo-readout system, including the digitizing readout electronics ($45k): Study of 25 APDs (final specification and cost). Design, construction and study of 25 fast charge-sensitive pre-amplifiers (final specification and cost). Study of new WFD prototypes (10-bit, 250 MHz).

R&D plans for Calorimeter (2004) Construction of new prototype of the Photon Calorimeter ($35k) Summer 2004 An array of 5  5 modules with the final version of module’s instrumentation. This prototype will be employed to test the performance of the pre-production modules and to adjust the specification for the digitizing system and other accompanying systems.

R&D plans for Calorimeter (2005) Spring 2005 Development of the conceptual and technical design of the Calorimeter system ($20k). Fall 2005 Construction of 10  10 mass-production modules array with appropriate pre-production prototypes of the digitizing, cooling and monitoring systems ($270k). In collaboration with those responsible for the Preradiator, this prototype will be employed to study the energy and timing performance of a joined Calorimeter/Preradiator system.

References KOPIO collaboration, “ Measurement of the decay K 0    ”, Technical Design Report for the National Science foundation, June 06, 2001, page 53. G. S. Atoian et al,, “ Preliminary Research for Shashlyk Calorimeter for E926 ”, KOPIO TN015, 15 June 1999, physics/ G.S. Atoian et al., “ Study of the energy resolution of the KOPIO Preradiator/Calorimeter system “, KOPIO TN034, 18 Apr 2002.tudy of the energy resolution of the KOPIO Preradiator/Calorimeter system Photon Calorimeter for KOPIO